BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / T	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
SPOT MARKET VOYAGE CHARTERS
Reserve against due from charterers	$ 1,400	$ 1,900
TIME CHARTERS
Unasserted claims relating to time charters	$ 0	400
VESSELS, NET
Estimated useful life of vessels	25 years
Estimated scrap value (in dollars per lightweight ton) | $ / T	325
Depreciation expense	$ 97,600	79,100	$ 41,600
VESSELS UNDER CONSTRUCTION
Capitalized interest costs	$ 3,163	27,602	35,170
IMPAIRMENT OF LONG-LIVED ASSETS
Industry average trailing period considered for forecasting future charter rates and vessel operating costs	10 years
Impairment of assets	$ 0	0	0
Vessels under construction.
VESSELS UNDER CONSTRUCTION
Capitalized interest costs	$ 3,200	$ 27,600	$ 35,200
Furniture and fixtures
OTHER FIXED ASSETS
Useful life	P10Y
Vessel Equipment
OTHER FIXED ASSETS
Useful life	P5Y
Vessel Equipment | Maximum
OTHER FIXED ASSETS
Useful life	P5Y
Computer Equipment
OTHER FIXED ASSETS
Useful life	P5Y